CAN (Controller Area Network) Principles
CAN is a multi-master, serial communication protocol used primarily in real-time applications such as automotive and industrial automation. It allows devices to communicate with each other without a central host. The main features of CAN include:
lMulti-master: Any device on the network can initiate communication.
lError detection: Has powerful error detection and handling mechanisms.
lReal-time: Suitable for real-time applications such as automotive electronic control units (ECUs).
CAN communication is based on the following key concepts:
lFrame type: CAN communication uses different types of frames, including data frames, remote frames, error frames, and overload frames. Data frames are used to transmit data, remote frames are used to request data, error frames are used to report errors, and overload frames are used to indicate internal buffer overloads.
lArbitration: CAN uses a non-destructive arbitration mechanism when multiple nodes try to send messages at the same time. Each message has a unique identifier, and in the binary representation of the identifier, the lower the bit value, the higher the priority.
lError detection and handling: CAN has powerful error detection mechanisms, including cyclic redundancy check (CRC), bit stuffing, and frame checking. If an error is detected, the sending node sends an error frame and retransmits the message.
CANopen Principle
CANopen is a high-level communication protocol based on CAN, which defines the communication rules of the application layer. CANopen not only provides a communication mechanism, but also defines the standards for device configuration and network management. Its main features include:
l Standardized communication objects: such as process data objects (PDO) and service data objects (SDO).
l Network management: Control the status of nodes through network management objects (NMT).
Device configuration: Device configuration is performed through device configuration files (DCF) and device sub-protocols.
CAN FD (Flexible Data rate) Principle
CAN FD is an extension of the CAN protocol. It increases the data transmission rate and data byte length while maintaining the original characteristics of the CAN protocol. The main improvements of CAN FD include:
lData transmission rate: The standard CAN rate is used in the arbitration phase, and it can be increased to a higher rate in the data phase. This allows more data to be transmitted when needed while maintaining the real-time nature of the network.
lData byte length: The data field is extended from 8 bytes to a maximum of 64 bytes, which increases the amount of data in a single communication, reduces the number of communications, and improves efficiency.
lCompatibility: CAN FD maintains compatibility with standard CAN, which means that CAN FD devices can communicate with standard CAN devices on the same network, although standard CAN devices cannot take advantage of the high-speed data transmission characteristics of CAN FD.
Differences between CAN, CANopen and CAN FD
- Hierarchical relationship:
-CAN: defines the communication rules of the physical layer and the data link layer.
-CANopen: built on CAN, defines the communication rules of the application layer.
-CAN FD: expands the data transmission capability of CAN and increases the data rate and length.
- Application scope:
-CAN: widely used in automobiles and industrial control.
-CANopen: particularly suitable for embedded networks that require standardized device configuration and network management.
-CAN FD: suitable for applications that require high-speed data transmission and large data volumes, such as advanced driver assistance systems (ADAS).
Actual use cases of each
- Automotive industry:
- CAN: used for traditional automotive control systems, such as engine management, brake systems, etc.
- CANopen: used for network communications within the car, such as door control, seat adjustment, etc.
- CAN FD: used for advanced driver assistance systems (ADAS) in modern cars, such as automatic emergency braking, lane keeping assist, etc.
- Industrial Automation:
- CAN: For communication between PLCs (Programmable Logic Controllers).
- CANopen: For equipment communication and control in industrial robots and automated production lines.
- CAN FD: In complex industrial automation systems that require high-speed data exchange, such as high-speed robot control, real-time monitoring systems, etc.
Through these cases, we can see that CAN, CANopen and CAN FD play their respective advantages in different application scenarios to meet different communication needs. With the development of technology, CAN FD is gradually being used in more fields due to its higher data transmission capacity and flexibility.